Electron scattering by whistler-mode ELF hiss in plasmaspheric plumes

Summers, Danny and Binbin, Ni and Meredith, Nigel P. and Horne, Richard B. and Thorne, Richard M. and Moldwin, Mark B. and Anderson, Roger R. (2008) Electron scattering by whistler-mode ELF hiss in plasmaspheric plumes. Journal of Geophysical Research, 113 (A04219). pp. 1-17. ISSN 2156-2202

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Abstract

Nonadiabatic loss processes of radiation belt energetic electrons include precipitation loss to the atmosphere due to pitch-angle scattering by various magnetospheric plasma wave modes. Here we consider electron precipitation loss due to pitch-angle scattering by whistler-mode ELF hiss in plasmaspheric plumes. Using wave observations and inferred plasma densities from the Plasma Wave Experiment on the Combined Release and Radiation Effects Satellite (CRRES), we analyze plume intervals for which well-determined hiss spectral intensities are available. We then select 14 representative plumes for detailed study, comprising 10 duskside plumes and 4 nonduskside plumes, with local hiss amplitudes ranging from maximum values of above 300 pT to minimum values of less than 1 pT. We estimate the electron loss timescale τloss due to pitch-angle scattering by hiss in each chosen plume as a function of L-shell and electron energy; τloss is calculated from quasi-linear theory as the inverse of the bounce-averaged diffusion rate evaluated at the equatorial loss cone angle. We find that pitch-angle scattering by hiss in plumes can be efficient for inducing precipitation loss of outer-zone electrons with energies throughout the range 100 keV to 1 MeV, though the magnitude of τloss can be highly dependent on wave power, L-shell, and electron energy. For 100- to 200-keV electrons, typically τloss ∼1 day while the minimum loss timescale (τloss)min ∼hours. For 500-keV to 1-MeV electrons, typically (τloss) min ∼days, while (τloss)min < 1 day in the case of large wave amplitude (∼100's pT). Apart from inducing direct precipitation loss of MeV electrons, scattering by hiss in plumes may reduce the generation of MeV electrons by depleting the lower energy electron seed population. Models of the dynamical variation of the outer-zone electron flux should incorporate electron precipitation loss induced by ELF hiss scattering in plasmaspheric plumes.

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